1in case of protic solvelnts the activation energy of SN1 rxn decreases so SN2 reactions are favored in weakly polar medium or aprotic medium
For a given secondary halide the SN2 rxn is favoured by aprotic solvents why?
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9 Answers
1Aprotic = no donation of H+.
for ex. DMF (dimethyl fluoride)
nucleophile gets weaker in presence of water
because solvation weakens the nucleophile...
its donating ability reduces.
but aprotic solvents dun solvate nu-.
so SN2 is favoured here.
DMF is a popular aprotic solvent..
(there was question on it in iit-2008 as well)
11also, solvents with high high dielectric constant helps in making more stable carbocation...
so in presence of water, SN2 tendency is more than SN1.
1if the nu- weakens, its lone pair donating ability reduces,
so, it will not have enuf force to attack the molecule from backwards.
also,
since i told above dat C+ is more stable in H2O, so C+ forms quickly...
resulting in SN1.
